feat: add per-provider allow_user_refund control and align wildcard matching

allow_user_refund:
- Add allow_user_refund field to PaymentProviderInstance ent schema
- Migration 103: ALTER TABLE payment_provider_instances ADD COLUMN
- Cascade logic: disabling refund_enabled auto-disables allow_user_refund
- User refund validation: check provider instance allows user refund
- Admin refund validation: check provider instance allows admin refund
- Subscription refund: deduct days on refund, rollback on failure
- New endpoint: GET /payment/orders/refund-eligible-providers
- Frontend: ToggleSwitch in ProviderCard/Dialog, cascade in SettingsView

Wildcard matching:
- Change findPricingForModel from "longest prefix wins" to "config order
  priority (first match wins)", aligning with channel service behavior

backend/internal/service/payment_config_providers.go

@@ -22,16 +22,17 @@ func (s *PaymentConfigService) ListProviderInstances(ctx context.Context) ([]*db
 
 // ProviderInstanceResponse is the API response for a provider instance.
 type ProviderInstanceResponse struct {
-	ID             int64             `json:"id"`
-	ProviderKey    string            `json:"provider_key"`
-	Name           string            `json:"name"`
-	Config         map[string]string `json:"config"`
-	SupportedTypes []string          `json:"supported_types"`
-	Limits         string            `json:"limits"`
-	Enabled        bool              `json:"enabled"`
-	RefundEnabled  bool              `json:"refund_enabled"`
-	SortOrder      int               `json:"sort_order"`
-	PaymentMode    string            `json:"payment_mode"`
+	ID              int64             `json:"id"`
+	ProviderKey     string            `json:"provider_key"`
+	Name            string            `json:"name"`
+	Config          map[string]string `json:"config"`
+	SupportedTypes  []string          `json:"supported_types"`
+	Limits          string            `json:"limits"`
+	Enabled         bool              `json:"enabled"`
+	RefundEnabled   bool              `json:"refund_enabled"`
+	AllowUserRefund bool              `json:"allow_user_refund"`
+	SortOrder       int               `json:"sort_order"`
+	PaymentMode     string            `json:"payment_mode"`
 }
 
 // ListProviderInstancesWithConfig returns provider instances with decrypted config.
@@ -47,7 +48,8 @@ func (s *PaymentConfigService) ListProviderInstancesWithConfig(ctx context.Conte
 			ID: int64(inst.ID), ProviderKey: inst.ProviderKey, Name: inst.Name,
 			SupportedTypes: splitTypes(inst.SupportedTypes), Limits: inst.Limits,
 			Enabled: inst.Enabled, RefundEnabled: inst.RefundEnabled,
-			SortOrder: inst.SortOrder, PaymentMode: inst.PaymentMode,
+			AllowUserRefund: inst.AllowUserRefund,
+			SortOrder:       inst.SortOrder, PaymentMode: inst.PaymentMode,
 		}
 		resp.Config, err = s.decryptAndMaskConfig(inst.Config)
 		if err != nil {
@@ -110,10 +112,12 @@ func (s *PaymentConfigService) CreateProviderInstance(ctx context.Context, req C
 	if err != nil {
 		return nil, err
 	}
+	allowUserRefund := req.AllowUserRefund && req.RefundEnabled
 	return s.entClient.PaymentProviderInstance.Create().
 		SetProviderKey(req.ProviderKey).SetName(req.Name).SetConfig(enc).
 		SetSupportedTypes(typesStr).SetEnabled(req.Enabled).SetPaymentMode(req.PaymentMode).
 		SetSortOrder(req.SortOrder).SetLimits(req.Limits).SetRefundEnabled(req.RefundEnabled).
+		SetAllowUserRefund(allowUserRefund).
 		Save(ctx)
 }
 
@@ -221,6 +225,21 @@ func (s *PaymentConfigService) UpdateProviderInstance(ctx context.Context, id in
 	}
 	if req.RefundEnabled != nil {
 		u.SetRefundEnabled(*req.RefundEnabled)
+		// Cascade: turning off refund_enabled also disables allow_user_refund
+		if !*req.RefundEnabled {
+			u.SetAllowUserRefund(false)
+		}
+	}
+	if req.AllowUserRefund != nil {
+		// Only allow enabling when refund_enabled is true
+		if *req.AllowUserRefund {
+			inst, err := s.entClient.PaymentProviderInstance.Get(ctx, id)
+			if err == nil && inst.RefundEnabled {
+				u.SetAllowUserRefund(true)
+			}
+		} else {
+			u.SetAllowUserRefund(false)
+		}
 	}
 	if req.PaymentMode != nil {
 		u.SetPaymentMode(*req.PaymentMode)
@@ -233,6 +252,7 @@ func (s *PaymentConfigService) GetUserRefundEligibleInstanceIDs(ctx context.Cont
 	instances, err := s.entClient.PaymentProviderInstance.Query().
 		Where(
 			paymentproviderinstance.RefundEnabledEQ(true),
+			paymentproviderinstance.AllowUserRefundEQ(true),
 		).Select(paymentproviderinstance.FieldID).All(ctx)
 	if err != nil {
 		return nil, err